DNA vaccines for H5N1 virus in development

Vaccines for the avian influenza H5N1 virus and
DNA-based vaccines proven to be capable of providing protection for various H5N1
strains are in development by scientists at the Academia
Sinica.

A team of researchers at Taiwan's leading academic body have also
discovered that once new virus strains are found, the strains' genetic
information can be incorporated into the vaccine database to produce new
vaccines that can induce immunity against new strains of
H5N1.

Hemagglutinin
The team, led by David Ho of the Rockefeller
University and Chi-huey Wong of Academia Sinica's Genomics Research Centre,
started its research two years ago with the focus on hemagglutinin, or HA -- a
type of glycoprotein molecule that can be found on the surface of all H5N1
viruses and plays a vital role in the viral infection process.

After
analysing hundreds of hemagglutinin samples that were collected from various
H5N1 strains, an identical gene sequence -- dubbed "Consensus HA" -- were found
on all specimens. The sequence was later genetically engineered to produce the
prototype vaccines.

During experiments, lab mice that have been
inoculated were found to develop immunity of various H5N1 strains, including the
strains found in Vietnam, Indonesia, Turkey, and southern China.

Survival rates
"When infected by the Indonesian strain of H5N1, 80
percent of the subject mice survived, " said Ting-jen Rachel Cheng of the
Genomics Research Centre. "Meanwhile, 100-percent survival rates were found
among all mice that were exposed to the other three strains."

DNA-based
vaccines, however, have one distinct drawback. "Based on the experiments (and)
research done by other scientists, DNA-based vaccines are prone to elicit weak
immune response, " said Chen Ming- wei, a post-graduate student at National
Yang-Ming University.

After further testing is completed by the end of
2008, the vaccine will be submitted to the U.S. Department of Health and the
Food and Drug Administration as a new drug awaiting human trials. Once approved,
the phase-I clinical trial in humans can be carried out.